This invention relates in general to sewing machines and in particular to a new and useful feed drive for the work holder of a zig-zag stitch group sewing machine.
The innovation relates particularly to a zig-zag stitch group sewing machine which contains a work holder movable by a cam plate parallel to the longitudinal direction of the housing arm and a needle bar moving up and down which executes lateral swinging movements controlled by the same cam plate, these swinging movements occurring crosswise to the longitudinal direction of the housing arm. The advantage of this movement direction of the work holder and of the needle bar common in buttonhole sewing machines generally is that their movement paths are straight. Also it is advantageous that the drive elements arranged between the work holder and the cam plate move essentially in a common plane, so that no moments occur between the work holder and its drive. With this type of machine, however, technical difficulties of handling exist if the zig-zag stitches to be executed by the needle bar extend crosswise to the longitudinal edge of the work. In this case, in fact, the longitudinal edge of the work runs parallel to the longitudinal direction of the housing arm, so that in particular for long pieces of material it may be difficult to handle the part of the work present under the housing arm. Also, it is not possible with such machines to to form transverse zig-zag bars, e.g. the fastening bars of belt loops, on tubular material.
U.S. Pat. No. 4,171,673 (German Pat. No. 29 25 253) teaches a stitch group sewing machine where, for the formation of relatively large seam patterns, the work holder is moved in longitudinal and transverse directions. The work holder is arranged at the end of a telescoping arm pivotably mounted in the region of the housing standard and is moved lengthwise and crosswise to the telescoping arm through two rope pulley drives driven by step motors. Connected with the two rope pulley drives is a compensating device which in case of a pure swinging movement of the telescoping arm transforms the arcuate path of the work holder into a rectilinear one.
Rectilinear guides for a work holder are known in themselves from U.S. Pat. No. 2,796,034 (German Pat. No. 1 092 284) but generally they form part of a three-dimensional cross slide system and are located laterally of or below the bearing surface for the work holder.